GeForce is an nvidia product, right? Have you tried running xorgwizard in the initial
black console (Alt-Ctrl-Backspace brings you there). Press the choose button. Then
you are offered the choice of the nouveau or nv drivers for nvidia video cards. Reboot
if necessary (if the Puppy doesn't do it automatically).

Upon reboot, a confirmation screen appears, presenting you with a wider choice of
resolutions.

I'm writing this on a Puppy Precise 5.7.1 and I am getting 1280x1024 res. from a very
old mmx GeForce 4400 with 64 Mg only, using the "simple" nv driver. So you may be
offered even better resolutions. (Although res. capacity depends on the monitor
capacity, too.)